B lymphocytes are the central component of the humoral immune response. Although B cells are activated and regulated through their cell-surface molecules, little is known about the structure of most B cell-restricted cell-surface proteins other than Ig. One human B cell structure, B1, is a phosphoprotein that generates a transmembrane signal which is involved in regulating B cell proliferation and differentiation. The gene that encodes the human B1 protein has been isolated demonstrating that B1 is structurally similar to two other phosphoproteins, rhodopsin and the B- adrenergic receptor. Also, the B1 gene may be associated with a chromosomal translocation that occurs in B cell malignancies. The aim of this project is to further examine B1 and other B cell- restricted cell surface molecules to determine their roles in B cell function. The first specific aim is to study the murine counterpart of B1 through the isolation of the murine B1 gene, the identification of the protein, and through studying the role of B1 in murine B cell function. Numerous murine models of human immunodeficiency syndromes exist, such as xid, lps, me, and scid, that will allow the study of B1 expression and function in genetically defined systems, and allow in vivo studies of B1 function. The murine B1 gene has been isolated and the structure of the protein will be determined by nucleotide sequence analysis. The B1 gene will be transfected into expression systems and sufficient B1 protein isolated to allow the production of monoclonal antibodies. These antibodies will be use to examine the function and structure of the B1 protein. The expression of the B1 gene and protein will be examined through the different stages of B cell ontogeny and development and compared with the expression of other surface structures such as Ig. The second specific aim of this project is to further characterize a collection of human B cell-specific cDNA clones that have been isolated which may also encode cell-surface structures. The structure and nucleotide sequences of these cDNA clones will be determined, as will their expression by B cells and cells of other lineages. Antibodies will be made against the protein products of these genes, and will be used to examined the roles of these proteins in B cell activation, proliferation, and differentiation. Determining the structural and functional characteristics of B cell-restricted proteins, in addition to B1, will provide a better understanding of how B cell function is regulated at the cell surface.